Source and prevention of fetal deaths in motor vehicle crashes

Fetal deaths were analyzed for how they occurred in motor vehicle crashes investigated by NHTSA (new research) and published findings were evaluated from side impact safety research (review of pertinent literature). The aim was to improve protection of the fetus and pregnant occupant.

Crashes involving fetal deaths were analyzed from the 2000-2015 NASS-CDS (National Automotive Sampling System-Crashworthiness Data System) and 2017-2022 CISS (Crash Investigation Sampling System). Each case was downloaded and summarized for the vehicle, pre-crash maneuvers, crash type, maternal seating position and injuries.

Eighteen (18) fetal deaths were available over 14 years and have a weighted incidence of 2,582 (184 ± 260 fetal deaths per year) in 2000-2018 model year vehicles. Near-side impacts were the most frequent crash type (57.8%) with the armrest-door the most common source (80.8%) of fetal death by loading the side of the pregnant abdomen. Several deaths involved side curtain and seat airbag deployments. The side airbags did not extend down over the armrest or extend forward enough leaving the pregnant abdomen without airbag coverage. Published sled tests with anesthetized animals found the abdomen was protected with a 1.1 kN crush force armrest in 32.2 km/h (20 mph) side-sled tests. A 3.7 kN crush force armrest caused AIS 4 (critical) injuries. The animal test results were confirmed in published side-sled tests with the BioSID dummy. Production vehicle armrests were tested in a published study. Eighteen of 20 (90%) had 9.5 ± 3.8 kN crush force. This is stiffer than the abdomen and deforms the abdomen in a side impact. An area of pregnant abdomens was defined on the side interior covering the 95^th percentile female at 9 months pregnancy. It extends 430 mm forward and 250 mm above the H-point of the 5^th female with the seat full rear and full down. The area requires energy absorbing materials or an airbag. Lap-shoulder belts were not a common source of fetal death. Modern seatbelts are sophisticated compared to those in 1980s-90s vehicles. Pretensioners tighten the lap belt on the thighs and the shoulder belt is load-limiting. Early research inferred seatbelt-related mechanisms for fetal deaths in frontal crashes. That inference is outdated with modern restraints.

The most beneficial area for fetal protection involves reducing side loading of the pregnant abdomen where larger airbag coverage and load-limiting side interiors are needed. Modern seatbelts with dual pretensioners are not a common source of fetal death.